1. Field of the Invention
The present invention relates to a porous electroformed shell for patterning and a manufacturing method thereof, and more particularly to a porous electroformed shell for patterning and a manufacturing method thereof, allowing to economically and effectively manufacture a surface skin material or plastic molded product with refined texture, which is employed in one-piece molding of a high-quality surface skin material for providing a curved surface of a specific three-dimensional cubic synthetic resin product with refined texture through various patterns of desired shapes and thereby enhancing an emotional quality.
In the manufacturing method of a porous electroformed shell for patterning, according to the present invention, both the overall and local formation positions, densities, and diameters of pores can be simply, economically, efficiently and precisely controlled according to various curved shapes of the electroformed shell by using a masking film. Accordingly, in forming the surface of a high-quality surface skin material (i.e. skin sheet or film) or a plastic molded product with a predetermined pattern, the predetermined pattern can be efficiently formed in such a manner as to have a regular position, a regular directionality, sharp radii, and minimized deformation by using the pores as decompression suction holes or air vents, which may be realized with increased productivity and economical efficiency.
2. Description of the Prior Art
With the improvement of the standard of living, and the industrial development, consumers have recently shown a tendency of gradually considering, as an important purchasing criteria, sensitive qualities (such as colors or textures) shown in a product's appearance as well as the product's own functions.
In accordance with such a tendency, a plastic molding technology and an apparatus thereof have recently been advanced day-by-day. Also, as a cost reduction and a high value addition are required in a vehicle manufacturing field and an information technology (IT) field, various in-mold forming methods and a multicomponents coinjection method have been suggested, and their application ranges have been rapidly expanded.
The in-mold forming method indicates a kind of forming method in which within one mold, various technologies, such as labeling, lamination, painting, coating, welding, surface protection, decoration, assembly, transfer printing, laser cutting, plasma processing, spray activation, or micro-structuring, are applied while a product is molded. Also, the in-mold forming method may be divided into in-mold lamination (IML), in-mold decoration (IMD), in-mold coating (IMC), in-mold transcription (IMT), and the like, according to the kinds of applied techniques.
Meanwhile, in the multicomponents coinjection method, a molded article is manufactured by combining different kinds or colors of polymer molding materials with each other and by using one or more molding machines and a specific molding system through a single process. The method representatively includes sandwich molding, over-molding, or the like.
The two highly-functional and highly-efficient injection molding methods as described above are not independent from each other. In actuality, in many cases, the two methods are mutually overlappingly employed.
In manufacturing interior materials for an automobile, one-piece molding of a high-quality surface skin material is applied to various articles, such as an instrument panel or board, a glove box, a console, a lower cover, a pillar, a door's internal panel, an airbag cover panel, or the like. Also, examples of the method may include: an in-mold injection compression forming method, in which a thermoplastic polyolefin (TPO) film (about 0.7 mm) and a foamed layer (about 3.0 mm) as skin materials of a surface decorative layer for providing grain patterns and soft feeling, and a polypropylene composite as a substrate are used, the preformed TPO skin layer is mounted within a mold by a robot, and foaming and pattern-decorating processes and a molding process are simultaneously carried out as a single process; an in-mold trimming lamination method, in which a skin material after being laser-cut is trimmed within a mold, thereby omitting a post-process trimming process; a post-process-unwanted hybridizing method in which injection molding of thermoplastic resin, and reaction molding of polyurethane are applied to a sheet trim of a premium automobile so as to provide an excellent soft touch effect and a high scratch resistance and a high UV resistance; a carpet surface decoration integral molding method, in which for an interior material of a carpet skin material, a carpet laminate is preformed and compression-molded as a single process, without a preforming process of the carpet skin material, thereby reducing the number of processes; and a multi-stage clamping control injection compression molding method, in which in a case where a skin material is a foam material, the skin material is placed within a mold by opening the mold, and is subjected to low pressure molding, and then the mold is compressed and re-opened to restore the skin material's thickness to be close to its original thickness.
Herein, in in-mold forming employing a skin material having a specific cubic pattern, for example, a natural or artificial leather grain pattern, since the skin material has an influence on an emotional quality, it has become an important issue to provide a predetermined cubic pattern to the skin material, and preform it into a predetermined three-dimensional shape. Examples of such a preforming method may include a positive type (male type) vacuum forming method, a negative type (female type) vacuum forming method, a polyurethane spray method, and a slush molding method.
Herein, a general positive (male) vacuum forming method is shown in FIG. 9. FIG. 9 is a mimetic diagram illustrating a conventional general positive type vacuum forming method for preforming a skin material as a decorative layer. In the method, a sheet 34 made of polyvinyl chloride (PVC) or acrylonitrile-butadiene-styrene (ABS) copolymer, which is pre-textured with a predetermined grain pattern 34a and is preheated, is in contact with a porous epoxy mold 30 formed with multiple fine pores 31. Herein, the porous epoxy mold 30 has a specific three-dimensional cubic shape and is supported and fixed by a base 32 formed with a decompression suction hole 33 in the center thereof. Through decompression suction, the sheet 34 formed with the grain pattern is pre-shaped in such a manner that it can correspond to the shape of the porous epoxy mold 30.
This method is advantageous in that productivity and economical efficiency are high. However, since the sheet 34 pre-patterned with the grain pattern 34a, in a softened state through pre-heating, comes in contact with the porous epoxy mold 30 having a complicated three-dimensional shape and is vacuum-sucked, there is a disadvantage in that the entire expression precision of grains (sharpness of a grain outline) is low, some grains locally disappear, and positions and directions of grains are irregularly changed.
Meanwhile, FIG. 10 is a mimetic diagram illustrating a conventional general negative type vacuum forming method for preforming a skin material as a decorative layer. In the method, a porous electroformed shell 1′ which includes an electrodeposited layer 20 having a grain patterned surface 20a and multiple fine pores 21 formed therein is mounted on a lower mold 40 having a decompression suction hole 41 in the center thereof. Then, a smoothened thermoplastic polyolefin (TPO) sheet 35 not formed with a grain pattern is softened through preheating, comes in contact with the porous electroformed shell 1′, and is decompression-sucked while pressed by an upper mold 50. As a result, a grain pattern is provided to the sheet and at the same time, the sheet is pre-shaped.
Accordingly, since the above described negative type vacuum forming method generally employs the porous electroformed shell 1′, there is an advantage in that the expression precision of grains (sharpness of a grain outline) is high, local disappearance of grains hardly occurs, deformation of grains is minimized, positions and directions of grains are regular, and productivity and economical efficiency are high. Thus, the method has been widely applied to the manufacturing of a skin material having a decorative layer.
Meanwhile, a polyurethane spray method for obtaining a preformed skin material by spraying polyurethane on a grain-patterned surface of a mold, followed by curing, and a slush molding method for obtaining a preformed skin material by heating and rotating a mold embedded with a predetermined amount of thermoplastic polyurethane slush, and coating and curing the melted resin within the front surface (internal surface) of a mold cavity, has an advantage in that the expression precision of grains is high and positions and directions of grains are regular, but has a disadvantage in that the productivity and the economical efficiency are low and the durability of the mold is reduced.
As described above, since in an in-mold forming method employing a skin material with a specific cubic pattern, for example, a grain pattern, the above mentioned negative type vacuum forming method may be applied. Hereinafter, a conventional manufacturing method for the porous electroformed shell 1′ to be applied to pre-forming of the skin material, especially, a porous nickel electroformed shell, the porous electroformed shell 1′, and a forming method of the skin material, will be described.
Japanese Patent Laid-Open HEI 02-225687 (laid open on 1990.09.07) discloses a method for manufacturing a breathable porous electroformed mold, which includes the steps of: electrostatic planting a short fiber on a silver mirror conductive film of a mandrel surface; forming a first electroformed layer in which the base of the short fiber is buried; layering a second electroformed layer for generating and growing a through hole from the leading end of the short fiber; peeling the first and second electroformed layers from the mandrel; and removing the short fiber. This method requires an additional electrostatic file planting apparatus, two-step electroforming processes controlled according to the length of a short fiber, and a short fiber removing process by combustion and/or solvent dissolution, and thus has a low productivity and a low economical efficiency. Furthermore, since it is difficult to locally control the planting density of a short fiber file (a forming position of a shell hole) in accordance with a three dimensional shape during electroforming, it is also difficult to locally control the hole density of the electroformed shell.
Also, U.S. Pat. No. 5,728,284 (1998.03.17) discloses a method for manufacturing a porous electroformed frame, in which an electroformed frame surface layer with no hole is electroformed; a fine straight hole having a narrow and predetermined diameter is formed by laser, electron beam, ion beam, electric discharge, or drilling; and an enlarged-diametric hole from the end of the fine straight hole is extended by electroforming so that the hole diameter cannot be enlarged even by a long-time surface friction. This method has an advantage in that it is theoretically possible to control the diameter of the fine straight hole and the whole/local density, but has a disadvantage in that physical processing of multiple fine straight holes is very complicated, uneconomic, and time consuming, thus is in actuality, not efficient at all.